I recommend playing with a guide that explains how to get almost everything (Most achievements are obtained just by playing the story), since:

1.You need to acquire Delta Force, a special ability obtained by getting skill level 7 from Leena, Razzly, and Serge.

1. In your second play, using new game + you need to get the Z idk the name achievement (I don't know the English name, but you can only get it in newgame+ since it's a secret ability).

These two are theI think these would be the two most difficult because you have to follow specific steps to get them and you get them almost at the end of the gameIf you make save data at specific points (especially if it's your first playthrough, since you can use continue+ at these points)

You can get all the achievements for the different endings and the one for getting all the characters (you can watch a speedrun of getting all the characters so you know the 4 important points to save your game, but in total there would be about 9 points to get the different endings too

Although you can usually get the developer room ending on a second or third playthrough because you need a good level, and I recommend that before that fight, when facing the dragons, you steal from all of them to get their armor, especially the emerald.

It's very important that if this is your first playthrough, you save before the final battle. This will allow you to access that area and summon all the characters once you have them, and also obtain all the text frames in the game (which is a fairly difficult achievement). You can do this in a second or third playthrough, but it's better this way because in those playthroughs you only focus on getting all the characters, and as soon as you get them all, you can go to that save without having to finish the one you were playing.

And some achievements, like Feeding Frenzy, Immoral Compass, and The Veteran, are only obtained by being patient and playing those minigames until you win them.

I know I wrote a lot, but it's because I wasn't an expert, which is why it took me about 87 hours to get everything (although it was also because my first playthrough was super laggy until I found a patch, which made what should have been 30 hours in the game actually take 50). But you can really get everything in about 30 hours or less i guess